The present invention relates generally to recording and reading data from magnetic storage media. More particularly, the present invention pertains to time-based servo for positioning a head relative to one or more tracks of magnetic storage media.
Data storage in magnetic storage media systems, e.g., a linear tape storage system, has arrived at the point where progress in density requires implementation of track following servo systems to allow narrower data tracks. For example, tape products without servo generally operate with far fewer tracks per cm than systems which utilize servo technology.
The recording and reading of data in tracks on magnetic storage media requires precise positioning of magnetic read/write heads. The read/write heads must be quickly moved to and centered over particular tracks as recording and reading of data is performed. The heads can record and read data as relative movement occurs between the heads and the magnetic storage media in a transducing direction, e.g., the movement of tape in a tape cartridge across a read/write head. The heads are moved from track to track across the width of the tape in a translating direction which is perpendicular to the transducing direction.
Generally, magnetic storage media devices that read and record data on magnetic media use servo control systems to properly position the data read/write heads in the translating direction, e.g., across the width of the tape, perpendicular to the transducing direction, e.g., a direction coincident with the length of the tape. The servo control system generally provides a position signal from one or more servo read heads that read cross width position control information recorded in one or more servo tracks on the magnetic storage media.
Conventional servo systems generally fall into a category referred to as boundary systems in which at least one servo track or servo track pattern extending along the length of the magnetic media, e.g., tape, is laterally divided into two or more regions, separated by linear boundaries. The distinct regions have different properties which can be detected by the servo read head. For example, the regions may be recorded at different frequencies or phases, or they may contain bursts occurring at distinct times. Generally, for example, the servo head elements straddle the boundary between the regions, and the ratio of the amplitude of the response of the servo head to each region provides the position signal upon which the track following servo operates.
Such boundary type servos and tape systems are particularly susceptible to errors in the position signal. For example, to provide sufficient lateral dynamic range, servo read head elements tend to be approximately as wide as a full servo track width. Servo head instabilities, head wear, localized debris on the head or tape, and media defects all contribute to temporary or long-term shifts in the spatial response of the servo head to the recorded servo pattern in the servo track.
To address the problems associated with boundary type servos in which such systems are particularly susceptible to errors in the position signal as described above, time-based servo systems for magnetic storage media have been described. U.S. Pat. No. 5,689,384 to Albrecht, et al., entitled xe2x80x9cTiming Based Servo System For Magnetic Tape Systems,xe2x80x9d issued Nov. 18, 1997, describes a track following servo control system for use with magnetic media tape systems which derives head position information from one or more specially patterned servo tracks. The servo patterns are comprised of magnetic transitions recorded at more than one azimuthal orientations in a servo track, such that the timing of the servo position signal pulses derived from reading the servo pattern are decoded to provide a position signal used by the servo system to position data heads over desired data tracks of the storage media.
For example, the servo pattern described in U.S. Pat. No. 5,689,384 may comprise straight transitions essentially perpendicular to the length of the track alternating with azimuthally inclined or sloped transitions. That is, the azimuthally included or sloped transitions may extend across the width of a track at an angle to the head transducing direction. The relative timing of transitions read by the servo read head varies linearly depending on the head position with respect to the center of the servo track. A position signal is generated by determining the ratio of two timing intervals. In particular, the ratio can be determined by normalizing the variable time interval between dissimilar transitions with the interval measured between like transitions. A read head that is narrow with respect to the width of the servo track pattern and the data track width can be used.
Such a time-based servo has numerous advantages over boundary servo systems. For example, such a time-based servo generally addresses the disadvantages associated with the use of wide servo read heads. However, such time-based servo systems, depending upon the type of time-based servo pattern recorded in the servo track and the method of recording such a time-based servo pattern, may be sensitive to tape speed variations at the time the servo pattern is recorded in the servo track. Because of the need to control tape speed variations when recording time-based servo patterns, specialized equipment which includes special speed control features is generally necessary to perform such time-based servo recording. As such, the time based servo recording process becomes complex and expensive. Further, during playback of data recorded on such magnetic storage media, the time-based servo, depending upon the type of servo pattern recorded in the servo track, may be sensitive to transverse tracking variations, e.g., across the width of the servo track.
A method of providing a servo track configuration according to the present invention includes providing at least one servo track with the at least one servo track having a width. A servo pattern is repeatedly recorded in the at least one servo track. Repeatedly recording the servo pattern includes repeating the simultaneous recording of first and second reference pattern lines and a track pattern line in the at least one servo track. Each of the first and second reference pattern lines has an identical predetermined geometry and extends across the width of the at least one servo track. Further, the track pattern line has a predetermined geometry that is different than the predetermined geometry of the first and second reference pattern lines and extends across the width of the at least one servo track.
In various embodiments of the method, providing the at least one servo track may include providing at least one servo track along at least a portion of the length of a tape; providing the at least one servo track may include providing at least one servo track continuously along the length of the tape; and simultaneous recording of the first and second reference pattern lines and the track pattern line may include recording the track pattern line between the first and second reference pattern lines, may include recording the first and second reference pattern lines adjacent to one another, may include recording parallel pattern lines extending across the width of servo track, may include recording parallel first and second servo reference pattern lines that are orthogonal to a center line of the servo track extending along a length thereof, or may include recording a sloped track pattern line forming an angle with the center line of the servo track.
A servo control system for positioning a magnetic head adjacent a surface of a moving magnetic storage medium is also provided. The system includes a head assembly having a servo read head for reading a repeated servo pattern recorded in a servo track of the storage medium and generating a read head signal representative of the servo pattern. A servo decode circuit receives the read head signal and generates a position signal based on the read head signal that indicates the position of the servo read head relative to the servo pattern. The system further includes a positioning actuator for positioning the head assembly relative to the storage medium and a controller that activates the positioning actuator as a function of the position signal. The servo decode circuit receives the read head signal generated from the repeated servo pattern as the servo read head is moved in a transducing direction along the storage medium. The servo pattern includes a first servo pattern reference region and a second servo pattern reference region. Each of the first and second servo pattern reference regions include at least one reference pattern line having a predetermined geometry extending across a width of the servo track. The predetermined geometry of the reference pattern lines in the first and second servo pattern reference regions are identical. The servo pattern further includes a servo pattern track region. The servo pattern track region includes at least one track pattern line having a predetermined geometry extending across the width of the servo track. The predetermined geometry of the at least one track pattern line in the servo pattern track region is different than the predetermined geometry of the reference pattern lines in the first and second servo pattern reference regions. The servo decode circuit determines a time interval between reference pattern lines in the first and second servo pattern reference regions and determines between the at least one track pattern line in the servo pattern track region and a reference pattern line in at least one of the servo pattern reference regions to generate the position signal.
A servo tracking data recording tape according to the present invention includes at least one data track extending along at least a portion of the length of the tape and at least one servo track extending along at least a portion of the length of the tape. The at least one servo track has a track width orthogonal to the length of the tape. Further, the at least one servo track includes a servo pattern repeated along at least the portion of the length of the tape. The servo pattern includes a first servo pattern reference region and a second servo pattern reference region. Each of the first and second servo pattern reference regions includes at least one reference pattern line having a predetermined geometry extending across the width of the servo track. The predetermined geometry of the reference pattern lines in the first and second pattern reference regions are identical. The servo pattern further includes a servo pattern track region. The servo pattern track region includes at least one track pattern line having a predetermined geometry extending across the width of the servo track. The predetermined geometry of the at least one track pattern line in the servo pattern track region is different than the predetermined geometry of the reference pattern lines in the first and second servo pattern reference regions.
In one embodiment of the tape, each of the first servo pattern reference region and the second servo pattern reference region include a plurality of reference pattern lines extending across the width of the servo track. The predetermined geometry of each of the plurality of reference pattern lines in each of the first and second pattern reference regions is the same. Further, the servo pattern track region includes a plurality of track pattern lines extending across the width of the servo track with the predetermined geometry of each of the plurality of track pattern lines in the servo pattern track region being the same.
A system for recording servo track information according to the present invention within a servo track extending along at least a portion of the length of a tape is also provided. The servo track has a track width orthogonal to the length of the tape. The system includes a servo write head. The servo write head includes a first and second reference write gap. Each of the first and second reference write gaps have substantially identical predetermined geometries. The servo write head further includes a track write gap. The track write gap has a predetermined geometry different than the predetermined geometry of the first and second reference write gaps. The system further includes means for moving the servo track of the tape and the servo write head relative to one another. The servo read head is selectively energized such that during energization first and second reference pattern lines and a track pattern line of a servo pattern are simultaneously recorded in the servo track. The first and second reference pattern lines are recorded by the first and second reference write gaps, respectively, across the width of the servo track and the track pattern line is recorded by the track write gap across the width of the servo track.
A servo write head apparatus for recording servo information in a servo track according to the present invention includes a head body and a first and second reference write gap defined in the head body. The length of each of the first and second write gaps allows for altering the state of the servo track across a width thereof. Each of the first and second reference write gaps have substantially identical predetermined geometries. Further, a track write gap is defined in the head body. The track write gap has a length allowing for altering the state of the servo track across the width thereof. The track write gap has a predetermined geometry different than the predetermined geometry of the first and second reference write gaps.
In various embodiments of the servo write system and servo write head apparatus, the track write gap may be located between the first and second reference write gaps, the first and second reference write gaps may be adjacent one another, the first and second reference write gaps may be parallel gaps, and the track write gap may be formed at an angle relative to the first and second reference write gaps.
A system and method for recording time-based servo track information within a servo track of tape in a tape cartridge is also provided according to the present invention. For example, this allows field erasure and servo recording for time-based servo as opposed to factory servo writing.